The long-term objective of this research is to determine how substances with adjuvant activity interact with lymphoid cells to influence their expression. Adjuvants are defined by their capacity to enhance cellular and humoral immune responses and thus are potentially of great practical use in cancer immunotherapy and in vaccination. However, substances with adjuvant activity also have the capacity to suppress immune responses. This laboratory recently showed that both bacterial endotoxin and a nucleic acid duplex can be extremely inhibitory to secondary antibody responses. The immediate objective of this study is to determine the lymphoid cell subpopulation required for this suppressive effect. This will be studied in the mouse using an in vitro secondary antibody response to soluble protein antigens. The cell type involved in suppression will then be compared to the cell type necessary for enhancement in order to begin to dissect the mechanisms employed by adjuvants in manipulating immune responses. Possible cell-free mediators of these various activities of substances with adjuvant activity will be sought.